1. Field of the Invention
The present invention relates to a sheet post-processing apparatus performing post-processing such as sorting and stapling and an image forming apparatus including the sheet post-processing apparatus.
2. Description of the Related Art
As a method of reducing a height of folded part in saddle stitching and center-folding in a sheet post-processing apparatus performing post-processing such as sorting and stapling, there is known, as disclosed in Japanese Patent Application Laid-open No. 2003-182928, a mechanism of housing sheets discharged from an image forming apparatus in an accumulating unit and center-folding a saddle stitched sheet bundle, the mechanism having a configuration in which a folding plate presses a central portion of the saddle-stitched sheet bundle in the conveying direction to push the central portion into a nip of a pair of first folding rollers to form a folded portion in the sheet bundle; the center-folded sheet bundle is stopped at a predetermined position; and subsequently, a second folding roller movable in a direction orthogonal to the sheet conveying direction runs on the folded portion while pressing the folded portion to increase intensity of folding.
As disclosed in Japanese Patent Application Laid-open No. 2010-006602, there is known a mechanism includes a pressing unit that is provided downstream of a folding unit folding a stitched sheet bundle in two and sandwiches a folded portion of the stitched sheet bundle, which has been folded in two, from a front and a back between press surfaces opposing each other to apply pressing pressure thereto, and a pressing count control unit setting the pressing count and controlling pressing operation, so that continuous pressurization can be performed when the pressing pressure is applied, and this pressing can be performed a plurality of times; as a result, even when the sheet bundle includes a great number of sheets, intensity of folding can be reliably increased by performing pressing an appropriately number of times depending on the number of sheets.
The conventional arts described above, for example, the configuration disclosed in Japanese Patent Application Laid-open No. 2003-182928 makes the second folding roller move in the direction orthogonal to the conveying direction relative to the folded portion after the sheet bundle is folded in two. Therefore, the structure disadvantageously becomes complex, is upsized and high-priced.
The mechanism of Japanese Patent Application Laid-open No. 2010-006602 is a mechanism of applying pressure to the sheet bundle it with the press from above and below after the sheet bundle is folded in two, and therefore, the machine is also disadvantageously upsized and high-priced. Also in increase of intensity of folding, pressing pressure is applied all over the sheet bundle folded in two and thus is dispersed to require longer pressing time and an increase number of times of pressing, which disadvantageously reduce the productivity.